Okay. I have now read HB's original post in its entirety and have understood what I should have before I tried to be smart in the first place.
I am not one of those who thinks that a quality wicket is necessarily one which gets a top order batsman. A great delivery is a great delivery whether bowled at Mike Gatting or Courtney Walsh. Sure, it may give greater satisfaction when it tricks a great player with all his skills and his experience but it is the same delivery which may get a tail ender. The fact that it was 'over-specified' for the tail ender doesnt make it any less a delivery.
Yes as a a generalisation one can 'assume' that the top order batsmen would require higher quality of deliveries to be fooled by than those at the bottom but it doesnt ned any elaboration to suggest the great extent of exception that exist to such generalisation.
You will get top order batsmen with ordinary deliveries and bowl great ones at tail enders and may or may not get a wicket.
I am reminded of a great bowler who when his captain applauded him all the way for running through the opposition on a helpful wicket said, :I wish you would applaud me on the days when I bowl as well as this or better but end up with none for hundred or more" (or words to that effect)
As far as whether the top 7 constitute the better batsmen. Well thats a safer assumption to make which is likely to be correct often enough to be used as a criteria to separate good batsmen from below average. The exceptions, in a big enough sample wont make much of a difference.
But it is the defining of a wicket taking delivery as necessarily a good delivery that I have an issue with as I have with the assumption that a delivery that gets a quality batsman is necessarily a quality delivery as against one that gets a poor batsman.
The QUALITY lies in the delivery and not in the wicket taken.
What the bowlers do is BOWL quality DELIVERIES which sometimes do, and sometimes dont, get them wickets.. The quality of the batsman whose wicket falls does not determine the quality of the bowlers effort which is what they are trying to determine.